CollectionView NSURL会话速度和重新加载

Question

当我下载时时预报和条件图标时，我对iOS和开发天气应用程序相当陌生。我已经能够用NSURL连接实现UICollection。但是，我有关于NSURL会话的速度/性能问题的问题。以下是两个问题：

1)下载和显示下载图标的速度非常慢(而且有非常小的图像)。这个下载过程可以花费5-10秒的时间。

2)当我设置一个按钮来重置集合时，所有的数据都会被重置，但是在下载新图像之前，现有的图像仍然保留。同样，这可能需要5-10秒的时间。

这是我的代码：

 - (NSInteger)collectionView:(UICollectionView *)collectionView numberOfItemsInSection:(NSInteger)section {
return self.hours.count;
 }


 - (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath{
static NSString *identifier = @"ConditionsCell";

ConditionsCollectionViewCell *cell = [collectionView dequeueReusableCellWithReuseIdentifier:identifier forIndexPath:indexPath];

cell.conditionsTime.text = [self.hours objectAtIndex:indexPath.row];
cell.conditionsTemp.text = [NSString stringWithFormat:@"%@°", [self.hoursTemp objectAtIndex:indexPath.row]];

NSURLSession *session = [NSURLSession sharedSession];
NSURLSessionDataTask *dataTask = [session dataTaskWithURL:[NSURL URLWithString:[self.hoursIcons objectAtIndex:indexPath.row]] completionHandler:^(NSData *data, NSURLResponse *response, NSError *error) {

    UIImage * serverImage = [UIImage imageWithData: data];
    cell.conditionsImage.image = serverImage;

}];

[dataTask resume];

return cell;

}

下面是按钮的IBAction并重新加载CollectionView：

 - (IBAction)selectDay:(UISegmentedControl *)sender {
if (sender.selectedSegmentIndex == 0)
{
    self.todayOrTomorrow = @"today";
}
else if (sender.selectedSegmentIndex == 1)
{
    self.todayOrTomorrow = @"tomorrow";
}

self.hours = [self hours];
self.hoursIcons = [self hoursIcons];
self.hoursTemp = [self hoursTemp];

[_collectionViewHours reloadData];
 }

Answer 1

您正在后台下载数据，但不更新主线程上的UI，请尝试下面的模式它将对您有所帮助。

- (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath{
static NSString *identifier = @"ConditionsCell";

ConditionsCollectionViewCell *cell = [collectionView     dequeueReusableCellWithReuseIdentifier:identifier forIndexPath:indexPath];

cell.conditionsTime.text = [self.hours objectAtIndex:indexPath.row];
cell.conditionsTemp.text = [NSString stringWithFormat:@"%@°", [self.hoursTemp     objectAtIndex:indexPath.row]];
cell.conditionsImage.image = [UIImage imageNamed:""];//reseting image

NSURLSession *session = [NSURLSession sharedSession];
NSURLSessionDataTask *dataTask = [session dataTaskWithURL:[NSURL URLWithString:    [self.hoursIcons objectAtIndex:indexPath.row]] completionHandler:^(NSData *data, NSURLResponse *response, NSError *error) {
@autoreleasepool {//autorelease pool for memory release
if (!error) {
//UIImage * serverImage = [UIImage imageWithData: data];//comment this extra variable and can increase memory overhead.

dispatch_async(dispatch_get_main_queue(), ^{
cell.conditionsImage.image = [UIImage imageWithData: data];//update UI

});

}}//autorelease pool

}];

[dataTask resume];

return cell;
}

它肯定会对你的第一部分有所帮助。

谢谢。